Generally, a photodetector is a device detecting an optical signal to convert into an electrical signal. The photodetector detects an optical signal through a method that generates electric charges according to the optical signal through a device including a photodiode and the like and detects a voltage variation depending on generation of the electric charges, thereby converting into a digital signal.
Specifically, the photodiode is a device detecting light using a PN junction of a semiconductor, and detects light using a phenomenon in which electrons and positive electric charge holes are generated to cause a flow of current when the light is incident on the photodiode.
A PIN diode, an avalanche photodiode (APD) and the like are mainly used as the photodiode, and the PIN photodiode has a structure in which an intrinsic semiconductor layer having large resistance due to fewer carriers is installed in the middle of a PN junction.
On the other hand, the APD includes an avalanche layer in the middle of a PN junction, in which carriers generated according to excitation of incident light collide with atoms in the avalanche layer by a high electric field to newly generate hole-electron pairs.
And the APD uses a principle that an avalanche effect is generated while these hole-electron pairs collide with each other to increase a photocurrent.
Because a bias voltage is required to detect a normal optical signal in such a photodiode, a voltage generator for applying a bias voltage is connected to the photodiode.
The known art related to the present disclosure is disclosed in Korean Patent Application No. 10-2007-0030945 (Publication date: Mar. 16, 2007, entitled of “Optical Detection Device”).